1. Field of the Invention
The present invention relates to a magnetooptical recording method for effecting magnetothermal recording and read-out utilizing a magnetic Kerr effect, and more particularly to a magnetooptical recording method for effecting verification by reading the recorded information simultaneously with the overwriting.
2. Related Background Art
The magnetooptical memory has been known as an erasable optical memory. Said magnetooptical memory has the advantages of achieving a higher density in recording and being capable of recording and reproduction without contact with the information recording surface, in comparison with the magnetic recording method utilizing solely a magnetic head, but is associated with the following two drawbacks that the recording speed is limited because the old information has to be erased prior to recording, and that the verification (confirmation of the recorded information) cannot be made at the time of recording. In order to cope with these problems, there is known a method of effecting the erasure, recording and verification simultaneously by means of three optical heads, but such a method requires a bulky apparatus having a high cost. Therefore, in order to increase the recording speed, there is known an overwriting method in which the new information is overwritten on the old information. For such overwriting, there are proposed, for example, a magnetic field modulating overwriting in which the recording is conducted under the irradiation of a continuous laser beam and the simultaneous application of a modulated magnetic field, and a light modulation overwriting in which the overwriting is achieved by a modulated laser beam in combination with an exchange-coupled laminated film. In these methods, however, the limitation in the recording speed is not sufficiently resolved since the verification has to be conducted after the recording operation.
In order to resolve the drawback of a slow recording speed in the magnetooptical memory it is effective to effect the verification simultaneously with the overwriting. In this case, the verification is conducted by detecting the reflected light of the laser beam irradiating the magnetooptical recording medium at the recording operation, reproducing the recorded information from said detected light, and to check whether the thus reproduced information coincides with the recording information. However, in the conventional light modulation overwriting, it is extremely difficult to effect the verification simultaneously with the recording, since the reflected light from the magnetooptical recording medium in the course of recording is modulated by the recording information, as the irradiating laser beam itself is modulated. Also in the magnetic modulation overwriting, in an area in front of the center of the recording light spot, the old information still remains because the recording layer of the magnetooptical recording medium is not heated to a temperature high enough for recording. For this reason, the reflected light from said recording medium in the course of a recording operation contains severe crosstalk from the old recorded information, so that it is difficult to effect the verification simultaneously with the recording operation.